Shoppers pushing their trolleys in the plentiful aisles of British supermarkets have grown used to grabbing African produce from the shelves.

Sainsbury's is among those which import green beans, mangetout and sugar snap peas from Zambia.

Food shortages are affecting many Malawians

The irony cannot have escaped those who see images of famine in Southern Africa on their television screens.

How can Zambia still be exporting food for Western dinner tables if there is famine at home?

As world leaders gather at World Summit on Sustainable Develoment in Johannesburg, many people question the role of economics in sorting developing countries' priorities.

Washed away

So far, southern Africa's famines have been blamed on floods and drought.

Rain has fallen at the wrong time, and floods have swept away the crops.

The region has already been devastated by Aids, which has increased vulnerability to food shortages.

Some governments lack foreign exchange to import food, while concerns have grown over standards of governance in the countries affected.

The question now is whether policies pushed by agencies such as the International Monetary Fund have made matters worse.

IMF to blame

Many developing countries fear that IMF funds could be withdrawn if they do not follow its advice.

This fear that cash lifelines could disappear is one of the bigger incentives to follow the guidelines of the poverty reduction and growth strategy programmes, devised by the international lender.

In recent years, these programmes have called for the state role in agriculture to be reduced.

The subsidised state marketing boards - which guaranteed country wide and cross-seasonal prices for food crops - have largely been dismantled and privatised.

Subsidies for fertiliser and agricultural inputs have disappeared.

In theory, the private sector should step forward to provide these services.

But Oxfam's Penny Fowler said: "In some of the more rural areas, there is no incentive for the private sector to take on that role, as it is not profitable for them.

"The issue is when government was doing it, it would make more of an effort to stabilise prices."

Trade campaigners also point to the fact that while African countries have been encouraged to abolish subsidies, American and European farmers still enjoy them.

Cash crops

At the same time, more countries have been increasing their production of crops for export.

The separation of domestic production from the production of these cash crops - which are not necessarily as dependent on rain as the perpetually thirsty maize - means it is no surprise that this produce still appears in supermarkets.

However, the cultivation of land for cash crops has always been a controversial issue.

While it is a good earner, some fear it marginalises smaller farmers and reduces the land available for domestic consumption.

"We have been seeing crops from Kenya, Zambia and Zimbabwe [for years] and there have not been food shortages," Christian Aid's Judith Melby said.

"It is very difficult to say there is a direct correlation between the food shortages and this land."

However, she added: "There is an ongoing debate about when you are looking at long term food security, should you reconsider use of land for cash crops."

The fact that exports are continuing is no surprise, points out Dr Christine Kinealy, a famine expert at the University of Central Lancashire.

In times of famine, she said, "food will always chase profit".

"There are always people who win during famine, people who have access to food, and markets," Ms Kinealy said.

"Effectively, what happened in the Irish famine happens in every famine - people keep hold of food supplies, release them slowly when prices are at a maximum."